Three-dimensional multi-gate structures, such as the fin-type field effect transistors (FinFETs), have been actively developed following the trend of scaling down the size of the semiconductor devices. The narrow strip(s) of semiconductor material fin of the FinFET is used to form source/drain and channel regions of the transistor, and the gate structure wrapping around the channel region further provides better electrical control over the channel. While the size of the semiconductor device keeps decreasing, the fin arrangement becomes tightened and the gate pitch is reduced.